1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices, and in particular, to a method of manufacturing semiconductor devices including a step of coating a resist superposing on a resist pattern which has been used as a mask for etching, so that the stripping of the resist of the upper layer side is prevented.
2. Description of the Prior Art
In a manufacturing process of a semiconductor device, a series of steps including coating of a resist, forming a resist pattern, etching by using the resist pattern as a mask, and stripping the resist are repeated. Accordingly, if this series of steps can be simplified, it will contribute to a reduction of time required for the overall manufacturing process to a great extent.
From the stand point of this view, a method is frequently employed in which without stripping the resist which has been used for etching, a resist for forming the next resist pattern is coated superposing on the previous resist.
However, when the resist is coated superposing on the previous resist, without stripping the previous resist which has been used for etching, a problem arises in which the adhesion between the lower layer side resist and the upper layer side resist is not satisfactory and the upper layer side resist is apt to be stripped.
The cause is considered to be that foreign atoms are mixed with a surface layer portion of the lower layer side resist due to the performance of the etching, and the coupling of the lower layer side resist with the upper layer side resist is disturbed, or that the surface tension of the lower layer side resist is increased as a result of subjecting to the etching precess.
To solve these problems, there is a method in which a surface layer portion of the lower layer side resist is etched or modified by treating the surface layer portion with a developing solution before coating the upper layer side resist. However, in this method, it is sure that the probability of causing the stripping of the upper layer side resist is reduced, however, it takes a time for removing the surface layer portion. As a result, in fact only a very shallow portion (about 10 to 20 .ANG.) of the lower layer side resist is removed, and the upper layer side resist will be stripped depending on a thickness of the surface modified portion of the lower layer side resist. Furthermore, since the stripping of the upper layer side resist is found at a point of time when a series of steps of coating, exposing, and developing has been finished, it is necessary to perform again another series of steps of stripping the resist, treating with a developing solution, coating a resist, exposing, and developing. Accordingly, there is a loss of a great amount of time.